Sage Agastya wanted to take two hills — Sivagiri and Sakthigiri — to his abode in the South and commissioned his disciple Idumban to carry them. Idumban bore the hills slung across his shoulders, in the form of a kavadi one on either side. When he was fatigued, he placed the kavadi near Palani to take rest.
At this stage, Subrahmanya or Muruga had been outwitted in a contest for going round the world. Ganapati had won the prized fruit (pomegranate or mango) by simply going round His parents. Long after, this, Subrahmanya came sweating on His peacock to find that the prize had already been given away. In anger, the frustrated child left the divine parents and came down to Tiru Avinankudi at the Adivaram (pronounced Adivâram. It means foot of the Sivagiri Hill). Siva pacified Him by saying that He (Subrahmanya) Himself was the fruit (pazham) of all wisdom and knowledge; nee —you. Hence the place was called 'Pazham Nee' or Palani. Later, He withdrew to the hill and settled there as a recluse in peace and solitude.
When Idumban resumed his journey, he could not lift the hill. Muruga had made it impossible for Idumban to make it. In the fierce battle that ensued, Idumban was killed but was later on restored to life. Idumban prayed that: whosoever carried on his shoulders the Kavadi, signifying the two hills and visited the temple on a vow, should be blessed and he should be given the privilege of standing sentinel at the entrance to the hill.
Hence we have the Idumban shrine halfway up the hill where every pilgrim is expected to offer obeisance to Idumban before entering the temple of Dandâyudhapani. Since then, pilgrims to Palani bring their offerings on their shoulders in a kavadi. The custom has spread from Palani to all Muruga shrines worldwide.
The Kavadi signifies the balance(Kavu+Thadi). The balance rod used to balance the load on both the sides.The world is of shiva and shakthi. Everyone of us has the shiva and shakthi nature within us (psychologically referred to animus and anima) and as per taoism is it referred to ying-yang.
The Kavadi signifies the balance between the shiva and shakti nature for its perfect unification. Here idumban refers to your indomitable power of will to carry and balance both the powers with a single purpose of attaining the ultimate.
Murugan representing the shiva-shakthi swaroopa thus manifested before idumban and accepted idumban to be a part of his divine jyothi.
Vetrivel Muruganukku Harohara